1. Field of the Invention
The present invention relates to an apparatus and a method for processing image, in which images corresponding to two image signals are synthesized to display the synthesized image on a single display screen, and especially to such an apparatus and method in which a synchronizing control of one of the image signals is made when carrying out a displaying step on the display screen, as well as an image processing program to be used in such an apparatus and method.
2. Description of the Related Art
There has recently been a demand that an image processing apparatus be utilized in various modes. Attention has therefore been given to a function of displaying images corresponding to two image signals on a single display screen. In a certain image processing apparatus having such a function, the respective image signals are separated for respective frame data serving as a unit for display control and stored in a frame memory, and there is made a control of the respective vertical synchronization timings to display the image corresponding to the two image signals. However, utilization of the different image signals may slightly fall out of synchronization as a practical matter.
In view of such a problem, there has been proposed measures called a “passing processing” to control the display timing of the two image signals. Application of the passing processing permits to skip a certain frame of one image signal corresponding to the frame of the other image signal or write twice the same frame, when there exists a deviation in synchronization of the two image signals. This makes it possible to display the images corresponding to the two image signals on the single display screen, even when these image signals are not synchronized with each other in an accurate manner.
However, when the above-mentioned passing processing is utilized, there may be a large possibility that the skipping of the frame or the double writing of the same frame frequently occurs in a state where a deviation exists in synchronization of the two image signals. Such a situation does not cause any major problems when displaying a static image, but causes the problems when displaying a dynamic image. More specifically, the dynamic image may ineptly be reproduced under the influence of the passing processing, thus causing a user to feel that something is wrong, contrary to a manufacturer's intention of displaying the dynamic image smoothly.